This disclosure relates to the use of a reserve battery to provide power for a subsea electrical power function such as in subsea oil and drilling applications where electrical power is needed for many purposes such as powering emergency blowout preventers, point of load electrical power distribution, hybrid power systems, supplemental power, critical system backup, etc. The invention is applicable to any subsea electrical power function requiring the use of a battery that may degrade over time, thus making it advantageous to use a reserve battery, which does not degrade until activation.
Over time, primary batteries degrade causing a decrease in the batteries' ability to hold a charge and to deliver the charge to a load. Due to the primary battery's state of activation, the battery will lose efficacy as the battery ages. Similarly, rechargeable batteries degrade over time. While rechargeable batteries have the ability to be recharged, these batteries lose their ability to hold the same amount of original charge as the battery ages and/or is used. Further, rechargeable batteries require knowledge that the battery needs to be recharged as well as the time/ability to recharge the battery.
Due to the harsh environments encountered in subsea (including deepwater) applications such as salt water and high external pressure, subsea critical power applications require an electrical power source capable of ultrahigh reliability and ultralow maintenance and ease of remote replacement without bringing the device to the surface. During critical power needs, for example the action of enabling or disabling flow, reserve batteries offer an ultrahigh reliable solution for subsea electrical power applications and are proven in high reliability applications such as guided munitions, torpedoes and sonobuoys dating back to the 1940s. In order to enable battery reliability, low maintenance and ease of remote replacement, typical reserve batteries require unique alterations.
In view of the above, it is desirable to provide an electrical power source for critical subsea applications utilizing a reserve battery that is easily and remotely replaceable. Reserve batteries are primary batteries which are inert until the battery is activated and used. More specifically, the active chemical components of a reserve battery are inactive until such time as the battery is needed, thus facilitating long storage life. Thus, reserve batteries are useful for applications requiring extended storage time because they avoid deterioration of the active materials during storage and eliminate the loss of capacity due to self discharge. Reserve batteries can be stored for 10 or more years and still provide full power when required.
It is thus desirable to provide a reserve battery to a subsea power application so as to provide a reservoir of reserve power, for example, to control the flow of oil/gas on an oil/gas rig. Specifically, there is a need to provide a battery that does not deteriorate when stored for long time periods so that the battery will be immediately ready for use in critical situations.